The United States has called the Myanmar military operation against the Rohingya population “ethnic cleansing” and threatened targeted sanctions against those responsible for what it called “horrendous atrocities”.

“The situation in northern Rakhine state constitutes ethnic cleansing against the Rohingya,” secretary of state Rex Tillerson said in a statement, using a term he avoided when visiting Myanmar last week.

“The United States will also pursue accountability through US law, including possible targeted sanctions” against those responsible for the alleged abuses, which have driven hundreds of thousands of Rohingya into neighbouring Bangladesh, he said.

On Thursday morning, the US embassy in Myanmar said it had temporarily suspended travel for American officials to parts of Rakhine state, citing concerns over potential protests after Tillerson’s comments.

In a further ratcheting up of pressure on Myanmar’s military and civilian leaders, the UN envoy on sexual violence in conflict said on Wednesday that alleged atrocities against Rohingya women and girls by the military may amount to war crimes, crimes against humanity and genocide.

Pramila Patten, who met many Rohingya victims of sexual violence in Bangladesh camps during a visit this month, said she fully endorses the assessment by UN human rights chief Zeid Ra’ad Al Hussein that Rohingya have been victims of “ethnic cleansing”.

Speaking at a news conference in New York, Patten said at a news conference that the widespread use of sexual violence “was clearly a driver and push factor” for more than 620,000 Rohingya to flee Myanmar. It was “also a calculated tool of terror aimed at the extermination and removal of the Rohingya as a group,” she added.

Rights monitors have accused Myanmar’s military of atrocities, including killings, mass rape and arson, against the stateless Rohingya during so-called clearance operations after attacks by Rohingya militants on 30 police posts and an army base in August.

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More than 600,000 Rohingya Muslims have fled Rakhine state in Buddhist-majority Myanmar since the crackdown which followed the insurgent attacks. Most have gone to Bangladesh.

“These abuses by some among the ... military, security forces, and local vigilantes have caused tremendous suffering and forced hundreds of thousands of men, women, and children to flee their homes,” Tillerson said.

While repeating US condemnation of the insurgent attacks, he added: “No provocation can justify the horrendous atrocities that have ensued.”

Myanmar’s two-year-old government, led by Nobel Peace Prize laureate Aung San Suu Kyi, has faced heavy international criticism for its response to the crisis, though it has no control over the generals with whom it shares power.

“It’s not a situation that is completely under her authority, but certainly we are counting on her to show leadership and also to work through the civilian government with the military to address the crisis,” a senior US official told reporters in a conference call.

The term “ethnic cleansing” is not defined in international or US law and does not inherently carry specific consequences, a second senior US official said on the call.

Murray Hiebert, a south-east Asia analyst with the Center for Strategic and International Studies thinktank in Washington, said the state department’s use of the term and threat of sanctions “will likely have limited to no impact on the ground.“

“It is likely to create more distrust between the United States and Myanmar’s military and government and push them closer to China, Russia, and its more authoritarian neighbors in southeast Asia,” he added.

A UN official in September described the military actions as a textbook case of “ethnic cleansing,” but until now the US has avoided the term.

Washington has sought to balance its wish to nurture the civilian government in Myanmar, where it competes for influence with China, with its desire to hold the military accountable for the abuses. US officials also worry that the mistreatment of the Rohingya Muslim minority may fuel radicalism.